Chapter 61 - European glacial landscapes from the Younger Dryas Stadial

Abstract

The cooling of the North Atlantic Ocean and weakening of the Atlantic Meridional Overturning Circulation 12,900 years ago caused abrupt cooling in North America and, especially, in Europe. This interrupted the Bølling–Allerød Interstadial (14.6–12.9ka), which was generally characterised by a warm and relatively wet climate that rapidly resulted in the retreat of the European Ice Sheet Complex (EISC) and mountain glaciers. This cold reversal, called the Younger Dryas (GS-1: ~12.9–11.7ka), was responsible for a limited reexpansion (and in some cases, reappearance) of the glaciers, despite the decline in precipitation. In the EISC, the Younger Dryas is well represented by continuous moraine ridges from the Norwegian coast, Oslofjorden, and south Sweden to south and south-east Finland and western Russia, accompanied by the development of sandar, deltaic sedimentation in large lakes, drumlins and eskers. In most of the European mountains, the Younger Dryas glaciers were restricted to the highest cirques, in north- and north-east-facing slopes, protected from insolation, and fed by snow avalanches in the cirque headwalls (e.g., in the Romanian Carpathians, the Tatra Mountains, the Apennines and most of the Iberian ranges, while some 2–6-km-long glacial tongues could be found in the Pyrenees). In the Alps, longer glacial tongues developed in the tributaries, while the main glaciers underwent a clear readvance. The consequence of this glacial readvance in the European mountains was the formation of high frontal moraines (sometimes several arcs) mainly composed of large boulders. Some of the glaciers evolved into debris covered glaciers, while the increase in debris supply from the cirque headwalls favoured the formation of rock glaciers.